Gardening seems to generate as many myths and murky hand-me-down tips as actual truths.

You've likely heard lots of them ("Lighten clay soil by adding sand," for example) and probably would be surprised to learn which ones aren't true (like that one).That's the gist of a new book called "Coffee for Roses" that Massachusetts garden writer C.L. Fornari wrote for Pittsburgh-based St. Lynn's Press.

Fornari admits to being long fascinated by stories such as how laying out sticks of chewing gum is the best way to get rid of groundhogs and that geraniums need to be hung upside down to save them over winter.

Her book lays out 71 myths and sets the story straight. Here are 10 common ones still floating around:

1.) "Plant roses with coffee grounds/banana peels/eggshells." None of those are harmful, but all do negligible good, says Fornari."If you don't like the garden to look like a garbage dump," she writes, "or if you're tired of hearing the crows scream, 'Eggshells! Eggshells! Eggshells!' as they swoop toward your roses at 5 a.m., place your kitchen scraps (but not meat or cheese) into a compost bin."Or at least bury them under mulch in the rose garden.

2.) "Always put a layer of rocks or clay shards in the bottom of a pot for drainage." This one's counter-productive.

View full sizeSkip the old advice about lining the bottom of pots with rocks or pot shards.George Weigel

Placing larger media under smaller-particle media causes moisture to back up in the smaller media until it's saturated (i.e. what you're trying to avoid).

Fill the pot with potting mix the whole way to the bottom, Fornari advises, pointing to how growers grow their containerized plants.

"If a drainage layer were necessary, don't you think the professional growers would be doing it?" she asks.

3.) "Coat or seal wounds on trees." Fornari says this one comes from a desire to help a wounded tree."Our plant has a boo-boo, so we rush to get out the bandages," she says.

The truth is that tar or paint traps moisture in wounds, increasing the chance of infection. And it retards the growth of callus tissue that helps heal the wound properly.

View full sizeDon't seal tree wounds with tar or paint... it can be counter-productive to healing.George Weigel

Just make a clean cut of any broken stubs, and let wounds dry and heal on their own, she advises.

4.) "You should always stake a newly planted tree." Trees benefit from staking only in very windy sites or if the tree is top-heavy – and even then only for a year at most.

"When it comes to root and stem growth," says Fornari, "the action of a trunk and canopy swaying in the wind makes a plant grow stronger."

Blowing over is a different story, but normal wind stress actually helps root growth.

You'd need to amend clay by 50 percent with sand to actually aid drainage. A better idea, says Fornari, is to add composted manure, chopped leaves or similar organic matter to the surface and let nature work it in gradually.

6.) "Fertilize flowers with a high-phosphorus fertilizer to encourage more flowering." Most soils have sufficient phosphorus, and adding more doesn't force-feed a plant or super-boost its flowering.

Adding more phosphorus to sufficient phosphorus is a waste of money and may pollute.

Fornari says most flowers prefer a fertilizer that's higher in nitrogen than either of the other two main nutrients listed on fertilizer labels – phosphorus and potassium.

7.) "A perennial garden is less work because the plants come up every year." Coming up every year doesn't translate into low-maintenance.

When you add all of the flower deadheading, propping up the "floppers," pulling weeds, dividing the spreaders and replacing the failures, "a perennial garden is the most high-maintenance flower bed you can plant," says Fornari.

By all means, plant perennials, she adds. Just don't expect to walk away with little or no effort.

8.) "Ants help peonies open." You're very likely to see ants crawling over peony buds just before they open. They're not on bud-opening duty, though. They're after nectar seeping from the buds.

"The truth is the bud will open on its own, insects or not," Fornari says. "The ants are only there for a shot of sugar."

View full sizeTilling the garden every year can harm soil structure and lead to more weeds.George Weigel

9.) "The soil in vegetable gardens needs to be turned every year." Digging actually disturbs soil structure and causes more of a weed problem as new weed seeds are constantly stirred to the surface.

Fornari advises "no-till" gardening by topping soil with organic matter and letting worms and nature work it in gradually.

10.) "Marigolds keep bugs out of the vegetable garden." They might make the vegetable garden look nice, but other than possibly repelling some nematodes in warm-climate regions, marigolds don't prevent bug problems, Fornari says.

They don't stop rabbits either as gardeners who have seen rabbit-chewed marigolds will tell you.

Interested in more myth-busting?Check out Dr. Linda Chalker-Scott's Horticultural Myths pages at Washington State University Extension.

Or read either of Chalker-Scott's books: "The Informed Gardener" (University of Washington Press, 2008) and "The Informed Gardener Blooms Again" (University of Washington Press, 2010).

Or read three titles by Dr. Jeff Gillman, horticulture professor at Central Piedmont Community College in North Carolina: "The Truth About Garden Remedies" (2008), "The Truth About Organic Gardening" (2008) and "Decoding Gardening Advice" (2012). All three are published by Timber Press.